Fuel cell systems commonly include a fuel processor to convert readily available hydrogen-containing fuels such as hydrocarbons and low molecular weight alcohols to a reformate containing molecular hydrogen which is reacted with oxygen in the fuel cell. Known processes for generating molecular hydrogen from hydrogen-containing fuels include steam reformation (SR), partial oxidation and autothermal reformation (ATR). In these processes the hydrogen-containing fuel is reacted with steam and/or oxygen in the presence of a catalyst. The catalytic reaction is conducted at an elevated temperature, and may be endothermic or exothermic depending on which process is used.
In order to maintain the catalyst at its optimum operating temperature, it is desirable to pre-heat the reactants before they contact the catalyst. In some fuel processors, the pre-heating of the gaseous reactants is accomplished, at least in part, by heat exchange with the hot gaseous reformate produced by the catalytic reaction. Therefore, fuel processors of this type will include a heat exchange section and a catalyst section.
An example of a known catalytic fuel processor is shown in International Publication No. WO 2004/059232 (Rong et al.). The fuel processor of Rong et al. includes a shell-and-tube heat exchanger for pre-heating the gaseous reactants by heat exchange with the hot reformate. The heat exchanger has a floating header which permits the heat exchanger tubes to expand axially, thereby reducing the potentially damaging effects of thermal stresses produced by differential thermal expansion of the tubes and the shells. However, the shell-and-tube construction of the Rong et al. fuel processor requires a large number of parts, and therefore has relatively high material and assembly costs. Also, the large number of parts means that there are many joints at which leaks may develop.
There is a need for a fuel processor which is simpler and less costly to produce, while retaining the ability to minimize thermal stresses.